7 replies to this topic

[stevelane]

998 Mini City - Standard engine.

 

I think I already have the answer to my own question but as a relative newbie I wanted to run my thoughts by you guys before taking any bits off and missing something obvious.

 

Back at the beginning of the year I changed the diff side cover gaskets due to an oil leak and replace the pot joint seals at the same time.

 

As soon as it was changed they were leaking immediately but was much improved so I thought "hey its a mini" and got on with it.

 

However this leak has got slowly worse, I should add it was in more than one place, and each time I leave the car overnight there is a substantial pool of oil under it.

 

So, last night, I got the front of the car on ramps, cleaned all of the excess off and the idea was to leave it and wait until it started dripping again and it would make it easier to locate. There was so much oil all over the bottom of the engine before that it would have been impossible to see where it was coming from.

 

However, its now been 24 hours and not a drop of oil has reappeared ( yes, I have checked there is some left  ) so this has made me think that its a moving part that causes the problem and my first thought is that the pot joint seals didn't take rather than the gaskets didn't seal properly as I first thought.

 

I have checked the usual places, gear linkage is dry apart from residue that has crept onto it. The sump plug shows no oil coming out either. The oil that I wiped off had covered both sides of the bottom of the engine so I ruled out timing cover and clutch seal as I would have thought they would only cover one side.

 

So my logic takes me to the fact that the oil is leaking from the pot joint seals and then spraying all over when the wheels are turning and the only reason it has been getting worse is that the residue has been building up over time.

 

Does this sound right or am I missing something obvious?

 

 

[Ethel]

Are you sure the leak isn't coming from elsewhere? As you say, oil hitting the pot joints will be thrown about the same as oil coming from the shaft seals. The tappet chest covers, breather or fuel pump are all possibilities, as is the rocker cover.

 

If it is diff seals or covers, underlying root causes could be incorrect diff shimming, or gaskets that don't match the shimming procedure followed - unlikely if the engine was previously unmolested, and likely to leak even if not run. Search or ask about diff shimming and the gasket options if this seems a possibilty from your car's history.

 

Worn diff cover bushes will allow the output shafts to wander off centre and let oil pass the seals that are distorted while it's happening. Levering the pot joints side to side may show up slack bushes.

[stevelane]

Pretty sure the oil is coming from the lower parts of the engine as there is nothing past the lip between the gearbox and the engine block (hope that makes sense)

 

When the cover gaskets leaked before I found them by doing the same, cleaning it all up and then watching and saw it seeping through after about twenty minutes.

 

I will investigate any movement whilst its up on ramps, thanks for the advice

[Spider]

Common places for oil leaks like you are seeing are from the diff side covers, usually because the side cover bushes are worn. The seals have only so much take up (which isn't much), so once the bushes wear a bit, the Pot Joint can move beyond the seal take up.

 

Tappet Covers are another common place to leak. There's two types of gaskets but they are not interchangeable! Also, don't over look the bolt that holds them on, there is a seal on them too.

 

Fuel Pump can leak, though not as common as the above. And of course the head gasket too, along with the rocker cover gasket.

[stevelane]

Tappet covers and fuel pump are all dry so I'm pretty sure this is pot joints now

Are the bushes easy to change or do they need machining in any way?

[Spider]

They do need machining after fitting.

 

Surely someone does these on an exchange basis?  If not, then there's a business opportunity for someone!!

[Coxie]

Clean the oil off then get the car sitting level again. Leave it running for a while so the oil warms up and thins and it should leak again and let you know where the problem is.

[dklawson]

As Ethel and Spider said, once the side cover bushes are worn the new seals will only help for a little while and then they will leak again.  As Spider said, the replacement bushes have to be machined to size after installation.  To be done properly... they have to be bored to fit the pot joints on your car, not an arbitrary value.

 

I have used the following method to find leaks in the past.  It will require a bit of investing in time and money but it does work.  

• Go to the parts store and inquire about UV dye to add to the oil.  There are complete kits or you can buy just the dye and use a "black light" from the DIY center.   (The light can be incandescent, fluorescent, or LED).   
• THOROUGHLY degrease your car's engine top to bottom, front to back, and underneath.  You want it as clean and oil free as you can get it.
• At dusk park the car in a dim area and turn off nearby lights.
• Add the UV dye to the engine oil, start the engine and let it idle.
• Turn on your black light and shine it on the engine while you patiently wait for the leak to reveal itself.
• As the dyed oil leaks out the location of the leak will become visible with the black light.  If nothing shows while idling, take the car on a short drive and when you return... use the light again to look for the source of the leak.

 

See the general product information in the links below.

UV Dye Kit Link

 

Replacement Dye for Kit Link

 

EDIT:  In the second link for the replacement dye... look at the application picture.  It illustrates how the dye will light up to reveal the source of the leak.

Edited by dklawson, 01 September 2015 - 12:07 PM.